Project Summary/Abstract Fatal opioid overdoses have increased dramatically over the past decade. Incarcerated men and women with a history of opioid use are at high-risk for overdose upon re-entry into the community. Effective methods of overdose prevention and linkage to community-based substance use treatment post-incarceration are needed. The criminal justice setting is an ideal location to implement opioid overdose prevention interventions due to the high rates of at-risk populations and the opportunities for education and intervention upon re-entry into the community. However, this setting poses significant structural barriers to implementing and sustaining interventions. The use of mobile technology offers an innovative approach to overcoming these barriers and preventing opioid overdose among at-risk men and women upon re-entry into the community post-incarceration. This study will be a Stage I pilot and feasibility study that will be the first to use mobile technology tools to prevent opioid overdose following incarceration. The proposed study seeks to develop and test two mobile platforms: (a) mobile health application intervention (MAI); and (b) text messaging intervention (SMS) and will compare them to standard of care (SOC). Both interventions will use motivational interviewing and harm reduction skills training prior to release from incarceration. The proposed method of opioid overdose prevention is expected to be an efficient and easily disseminable platform that will facilitate linkage to community-based resources, increase knowledge and behavioral skills regarding opioid overdose prevention, and prevent the occurrence of opioid overdose among a key population during a particularly vulnerable period of time. A three-phase, top-down research approach to adapt, refine, and pilot test the interventions will be conducted. Phase 1 will include individual interviews (IDIs) with the target population and key stakeholders in the criminal justice setting to inform intervention development and the implementation strategy. Phase 2 will include development of the mobile intervention technologies. We will conduct a beta test and a series of IDIs with the target population and key stakeholders to inform iterative revision of the interventions. During Phase 3, we will evaluate the feasibility, acceptability, and preliminary efficacy of the mobile technology tools among men and women at-risk for opioid overdose upon re-entry into the community post-incarceration via a 3-armed (MAI vs. SMS vs. SOC) randomized controlled trial with 90 participants. Data will be collected regarding recent drug use, overdose risk behaviors, and linkage to community-based substance use services at 1-, 3-, 6- and 12-month follow-ups. Through IDIs, we will explore: (1) the difference between individuals who demonstrate high usage patterns of the intervention technologies and those with low usage patterns; (2) barriers and facilitators related to implementation and sustainability within the criminal justice setting; and (3) the relationship between outcomes and usage of the intervention technologies. The project is significant in regards to its potential to prevent opioid overdose among criminal justice populations and gain greater understanding of the utility of two mhealth intervention modalities.